Deleting characters from strings

This is a discussion on Deleting characters from strings within the C Programming forums, part of the General Programming Boards category; I'm trying to make a simple spelling corrector and I'm having some trouble. Let's say I have: "This is a ...

  1. #1
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    Deleting characters from strings

    I'm trying to make a simple spelling corrector and I'm having some trouble.

    Let's say I have: "This is a spelling corrector."
    How can I write a function to delete the unnessecary spaces in the string? I tried strncpy but I don't know how to skipthe spaces while copying.

    And a second question.
    We have: "This is is a spelling corrector."
    How do I delete the second 'is'?

    I'm new with C so I would apprecciate it if you guys would keep the explanation simple.

    Thanks in advance.

  2. #2
    vae victus! skorman00's Avatar
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    This isn't a C problem, this is a general logic problem.

    For the space, you can copy to a new string character by character. If there's a space, do nothing and move on to the next. For the "is is" problem, you can break the sentence into tokens (meaning each word would be by itself) and compare all of those. Remove the doubles that are next to each other, then rebuild the sentence.

    If you're still unsure as to what needs to be done, perhaps you're trying to tackle a problem that's a bit to tough for you just yet (don't take that as an insult).

  3. #3
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    Code:
    #include <stdio.h>
    #include <string.h>
    #include <ctype.h>
    #define MAXLINE 128
    
    int read_a_line(char * line);
    int the_end(char*line);
    void add_punct(char*line);
    void capitalize(char*line);
    void misspelling(char*line);
    
    
    
    void main() {
    char line[MAXLINE +1];
    printf("---Welcome to my amazing spelling corrector---");
    printf("\n\n-> Type 'end' when finished.");
    printf("\n\nType line:");
    while (1){
    read_a_line(line);
    capitalize(line);
    misspelling(line);
    add_punct(line);
    if (the_end(line));
    break;
    
    }
    printf("Corrected: %s\n", line);
    }
    int read_a_line(char line[]){
    char c;
    int length=0;
    while ((c = getchar()) != '\n' && length  <=MAXLINE){
    line[length++]=c; }
    line[length]='\0';
    return length;
    }
    int the_end(char*line){
    return strcmp(line, "end") == 0;
    }
    void capitalize(char*line){
    line[0]=toupper(line[0]);
    }
    void misspelling(char*line){
    int j;
    for(j = 0; line[j] != '\0'; j++) {
    if(line[j-1] == 'e' && line[j] == 'b' && (isspace(line[j+1])  || line[j+1]=='\0')){
    line[j-1] = 'b'; line[j] = 'e';  }
    if(line[j-1] == 's' && line[j] == 'i' && (isspace(line[j+1])  || line[j+1]=='\0')){
    line[j-1] = 'i'; line[j] = 's';  }
    if(line[j-1] == 't' && line[j] == 'e' && line[j+1] == 'h' && (isspace(line[j+2])  || line[j+2]=='\0')){
    line[j-1] = 't'; line[j] = 'h'; line [j+1] = 'e';   }
      }
    }
    void add_punct(char*line){
    int i;
    for(i = 0; line[i] != '\0'; i++)
    if(!ispunct(line[i])&& line[i+1] == '\0'){
    line[i+1] = '.'; line[i+2] = '\0';
      }
    }
    This is what I got so far. Skorman can you write those two little functions so I can see how it should be done? The best way to learn something is seeing it .

  4. #4
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    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    void erase( char *str, char chr );
    
    int main( void )
    {
        char test[] = "hello my brother's name is bob the builder!";
        
        printf( "%s\n", test );
        erase( test, 'b' );
        printf( "%s\n", test );
        getchar( );
        return 0;
    }
    
    void erase( char *str, char chr )
    {
        int i, pos = 0;
        for ( i = 0; str[i]; i ++ ) {
            if ( str [i] == chr ) {
                str[pos] = str[i + 1];
            } else {
                str[pos] = str[i];
                pos ++;
            }    
        }    
        str[pos] = '\0';
    }
    This erase function removes all occurances of a character from a string. When it encounters the character it simply overwrites it with the next character in the string. You might want to try indenting, and not using void main.

    (edit: oops fixed a bug with erase).
    Last edited by Brian; 11-09-2004 at 04:27 AM.

  5. #5
    Gawking at stupidity
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    Or more simply (I think):
    Code:
    void erase(char *str, char chr)
    {
      while(*str)
      {
        if(*str == chr)
          memmove(str, str+1, strlen(str));
        else
          str++;
      }
    }
    If you understand what you're doing, you're not learning anything.

  6. #6
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    Quote Originally Posted by itsme86
    Or more simply (I think):
    Code:
    void erase(char *str, char chr)
    {
      while(*str)
      {
        if(*str == chr)
          memmove(str, str+1, strlen(str));
        else
          str++;
      }
    }
    It looks simpler, but is slower. Mine only does strlen(str) iterations. Without calling any external functions such as memmove or strlen, which in turn have their own loops.
    Last edited by Brian; 11-09-2004 at 06:12 AM.

  7. #7
    #include<xErath.h> xErath's Avatar
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    If you want to really chech the spelling you 1st have to separate the whole string in tokens, then compare each one with the next.

  8. #8
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    Code:
    static char *
    erase(char *const string, const char c)
    {
            register char   *src;
            register char   *dst;
    
    
            for (src = dst = string; *src != '\0'; src++)
                    if (*src != c)
                            *dst++ = *src;
            *dst = '\0';
    
            return string;
    }

  9. #9
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    Ok I got the spaces but how do you integrate the words erase in this code?

    Code:
      #include <stdio.h>
    #include <string.h>
    #include <ctype.h>
    #define MAXLINE 128
    
    int read_a_line(char * line);
    int the_end(char*line);
    void add_punct(char*line);
    void capitalize(char*line);
    void misspelling(char*line);
    void spaces(char*line);
    
    
    
    void main() {
    char line[MAXLINE +1];
    printf("---Welcome to Murat Soyal's amazing spelling corrector---");
    printf("\n\n-> Type 'end' when finished.");
    printf("\n\nType line:");
    while (1){
    read_a_line(line);
    capitalize(line);
    misspelling(line);
    add_punct(line);
    spaces(line);
    if (the_end(line));
    break;
    
    }
    printf("Corrected: %s\n", line);
    }
    int read_a_line(char line[]){
    char c;
    int length=0;
    while ((c = getchar()) != '\n' && length  <=MAXLINE){
    line[length++]=c; }
    line[length]='\0';
    return length;
    }
    int the_end(char*line){
    return strcmp(line, "end") == 0;
    }
    void capitalize(char*line){
    line[0]=toupper(line[0]);
    }
    void misspelling(char*line){
    int j;
    for(j = 0; line[j] != '\0'; j++) {
    if(line[j-1] == 'e' && line[j] == 'b' && (isspace(line[j+1])  || line[j+1]=='\0' || ispunct(line[j+1]))){
    line[j-1] = 'b'; line[j] = 'e';  }
    if(line[j-1] == 's' && line[j] == 'i' && (isspace(line[j+1])  || line[j+1]=='\0')){
    line[j-1] = 'i'; line[j] = 's';  }
    if(line[j-1] == 't' && line[j] == 'e' && line[j+1] == 'h' && (isspace(line[j+2])  || line[j+2]=='\0' || ispunct(line[j+1]))){
    line[j-1] = 't'; line[j] = 'h'; line [j+1] = 'e';   }
      }
    }
    void add_punct(char*line){
    int i;
    for(i = 0; line[i] != '\0'; i++)
    if(!ispunct(line[i])&& line[i+1] == '\0'){
    line[i+1] = '.'; line[i+2] = '\0';
      }
    }
    void spaces(char*line)
    {
        int i, pos = 0;
        for ( i = 0; line[i]; i ++ ) {
            if ( isspace(line[i])) {
                line[pos] = line[i + 1];
            } else {
                line[pos] = line[i];
                pos ++;
            }
        }
        line[pos] = '\0';
    }

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